The present invention relates to a deflection circuit for the deflection coils of a television receiver.
Present techniques for powering vertical deflection coils of television receivers employ predominantly low voltage vertical deflection circuits. In general, such circuits comprise a sawtooth generator and a driver circuit, the output of which is connected to a linear output amplifier. The sawtooth generator employs a conventional integrated circuit comprising the elementary circuit groups of oscillator, feedback oscillator and voltage control circuit. The generator is synchronized by the vertical synchronizing pulses, providing for vertical deflection according to the existing picture cycle frequency.
During the sweep a time linear sawtooth shaped deflection current is generated in the deflection coil, which is in operation slightly S-shaped and which contributes to the compensation of possible tangent errors. During the sweep the voltage runs like the deflection current linearly with time. However, during retrace the voltage is proportional to the rate of current change of the deflection current resulting in a noticeable increase in voltage during return. Consequently, a higher operating voltage has to be applied to the vertical output amplifier during flyback in order to meet the return time. For this purpose conventional circuits provide for nearly doubling of the applied operating voltage through a voltage doubling circuit, although the really necessary voltage increase is considerably lower. Therefore, conventional vertical output amplifiers have to be constructed with expensive voltage proof devices in the output amplifier. Employing a conventional voltage doubling circuit results in the disadvantage of generating relatively high charge and recharging losses when the voltage is increased. Applying the higher operation voltages during sweep and retrace results in a high power loss in the output amplifier during the sweep, which generates heat which in turn has to be removed by providing appropriate cooling fins to the circuit casing.